1. Field of Invention
The present invention relates to an image processing method and apparatus utilizing a design of a hardware circuit or a program to execute color enhancement and correction, and more particularly to an image processing method and apparatus utilizing a chromaticity diagram in different color space to process digital color image data for color enhancement and correction.
2. Description of Related Arts
There are a variety of conventional image processing techniques for processing color enhancement and correction of digital color image data. In conventional image processing, many color scales, so called “color spaces,” are used in various conventional image processing techniques to process color enhancement and correction of digital color image data. However, a variety of conventional image processing techniques usually utilize an independent color space to convey color values in numerical terms. In other words, an independent color space is used as an intermediate representation of the image. For example, this color scale or “color space” is known as RGB (Red, Green, and Blue) color space. Other color spaces are known, such as CMY (cyan, magenta, yellow) color space, CMYK (cyan, magenta, yellow, and black) color space, YIN (luminance and chrominance) color space, . . . etc. Conventional image processing techniques usually utilize the color look up table (CLUT) method and the piecewise linear approximation method to implement color enhancement and correction of digital color image data.
In the color look up table (CLUT) method, a threshold value of the pixel of interest corresponding to a point of skin of a person's image in most cases is predetermined. Similarly, as to such object images as blue sky and green leaves of trees, a threshold value of the pixel of interest corresponding to a point of such object images is predefined. An object applicable to image processing and conditions thereof are specified and then image processing is carried out for object pixels. If the value of the object pixel is within a range of the threshold value, the value of the object pixel could be adjusted as desired by means of the CLUT. FIG. 1 is a graph showing a conversion relationship of a color look up table (CLUT). It may be necessary to load specific color look-up table entries from external memory to on-chip memory before a color look-up table (CLUT) is utilized. Hence the difficulty and problem associated with conventional image processing techniques utilizing the color look up table (CLUT) method is that sufficient memory is necessary for storing the color look-up table (CLUT). It will waste a lot of memories.
As shown in FIG. 2, in the piecewise linear approximation method, each of digital image data can be divided into several line segments of object pixels with slope discontinuities. Color enhancement and correction of each line segment of object pixels could be adjusted by means of the different slope of the line segment in the piecewise linear approximation method. Although the color enhancement and correction of a digital image data in the piecewise linear approximation method provides a desired effect on the digital image data, it may cause an undesired side effect thereon. The main difference between the color look up table (CLUT) method and the piecewise linear approximation method is that the color enhancement and correction of a digital image data in the piecewise linear approximation method causes an inharmonic side effect thereon.